The effects of hyperosmolar solutions on isolated vascular smooth muscle examined with verapamil.

Hyperosmotic sucrose solutions elicited tension from rat aortic strips in direct proportion to osmolarity. Norepinephrine-induced tension was reduced in proportion to increases in osmolarity; however, reduction of barium-induced tension by hyperosmolar solutions was minimal. Norepinephrine-induced tension is primarily dependent on intracellular calcium mobilization, while barium-induced tension is primarily dependent on extracellular calcium influx. Therefore, hyperosmolar solutions may alter vasoconstriction associated with intracellular calcium mobilization rather than that associated with extracellular calcium influx. In the presence of verapamil which blocks calcium entry into muscle, barium-induced tension was eliminated while the direct tension elicited by hyperosmolar solutions was slightly affected (6% reduction) and the inhibitory effect of hyperosmolar solutions on norepinephrine-induced tension was still observed. In contrast, the tension elicited by hyperosmolar solutions was greatly reduced by papaverine which promotes sequestration of myoplasmic calcium to cause relaxation. The vascular effects of hyperosmolar solutions may be due to alterations in the intracellular calcium rather than the extracellular calcium utilized by vasoconstricting agents.